Systems and methods for electrosurgical treatment of tissue in the brain and spinal cord

ABSTRACT

The present invention provides systems and methods for selectively applying electrical energy to a target location within a patient&#39;s brain and spinal cord. The systems and methods of the present invention are particularly useful for treating cerebrovascular diseases, such as vessel occlusion, or for the volumetric removal or ablation of intracranial tumors or Arteriovenous Malformations (AVMs). The method of the present invention comprises positioning an electrosurgical probe or catheter adjacent the target site so that one or more electrode terminal(s) are brought into at least partial contact or close proximity with a body structure within the patient&#39;s head or neck, such as tumor tissue or an occlusion within a blood vessel. High frequency voltage is then applied between the electrode terminal(s) and one or more return electrode(s) to volumetrically remove or ablate at least a portion of the body structure in situ. In specific embodiments, the high frequency voltage is sufficient to effect the dissociation or disintegration of organic molecules into non-viable atoms and molecules. Specifically, the present invention converts the solid tissue cells into non-condensable gases that are no longer intact or viable, and thus, not capable of spreading viral or bacterial particles to other portions of the body structure.

RELATED APPLICATIONS

The present application is a continuation-in-part of U.S. patentapplication Ser. No. 09/026,851, filed Feb. 20, 1998, now U.S. Pat. No.6,277,112 the complete disclosure of which is incorporated herein byreference for all purposes. The application also derives priority fromU.S. patent application Ser. No. 08/795,686, filed Nov. 22, 1995, thecomplete disclosure of which is incorporated herein by reference for allpurposes.

The present invention is related to commonly assigned co-pending U.S.patent application Ser. No. 08/990,374, filed Dec. 15, 1997, which is acontinuation-in-part of U.S. patent application Ser. No. 08/485,219,filed on Jun. 7, 1995, now U.S. Pat. No. 5,697,281, patent applicationSer. Nos. 09/109,219, 09/058,571, 08/874,173 and 09/002,315, filed onJun. 30, 1998, Apr. 10, 1998, Jun. 13, 1997, and Jan. 2, 1998,respectively and U.S. patent application Ser. No. 09/054,323, filed onApr. 2, 1998, U.S. patent application Ser. No. 09/010,382, filed Jan.21, 1998, and U.S. patent application Ser. No. 09/032,375, filed Feb.27, 1998, U.S. patent application Ser. Nos. 08/977,845, filed on Nov.25, 1997, 08/942,580, filed on Oct. 2, 1997, U.S. application Ser. No.08/753,227, filed on Nov. 22, 1996, U.S. application Ser. No.08/687,792, filed on Jul. 18, 1996, and PCT International Application,U.S. National Phase Ser. No. PCT/US94/05168, filed on May 10, 1994, nowU.S. Pat. No. 5,697,909, which was a continuation-in-part of U.S. patentapplication Ser. No. 08/059,681, filed on May 10, 1993, which was acontinuation-in-part of U.S. patent application Ser. No. 07/958,977,filed on Oct. 9, 1992 which was a continuation-in-part of U.S. patentapplication Ser. No. 07/817,575, filed on Jan. 7, 1992, the completedisclosures of which are incorporated herein by reference for allpurposes. The present invention is also related to commonly assignedU.S. Pat. No. 5,683,366, filed Nov. 22, 1995, the complete disclosure ofwhich is incorporated herein by reference for all purposes.

BACKGROUND OF THE INVENTION

The present invention relates generally to the field of electrosurgery,and more particularly to surgical devices and methods which employ highfrequency electrical energy to treat tissue in regions of the head andneck, such as the brain and spinal cord.

Cerebrovascular diseases are those in which brain diseases occursecondary to the pathological disorder of blood vessels (usuallyarteries) or the blood supply. This pathological disorder has a varietyof mechanisms, including vessel occlusion by thrombus or embolus,rupture or disease of the blood vessel wall and disturbances in thenormal properties of blood flowing through the brain. Regardless of themechanism, the resultant effect on the brain is eitherischaemia/infarction or haemorrhagic disruption (i.e., stroke).

Medical treatment for cerebrovascular disease has included anticoagulanttherapy and the use of thrombolytic agents. The effectiveness ofanticoagulant agents is uncertain and the risk of recurrent embolicinfarction is high. Similarly, thrombolytic agents pose a relativelyhigh risk of intracranial hemorrhage.

Surgical treatment for vascular diseases has included a number ofcatheter-based approaches, such as balloon angioplasty and endartectomy.Endartectomy procedures typically involve introducing a catheter havinga cup-shaped rotating cutter into the vascular system to sever andcapture at least a portion of the occlusive material. Otherinterventional techniques includes laser ablation, mechanical abrasion,chemical dissolution, hot-tipped catheters, drill-tipped catheters andthe like. While promising, these techniques have a few drawbacks. Forsome of these techniques (e.g., balloon angioplasty), it is oftendifficult to advance the distal end of the catheter through the stenosedregion in extremely narrow vessels, such as those encountered in thebrain. Under these circumstances, it may be necessary to at leastpartially recanalize the occlusion before the catheter procedure canbegin. Other techniques (e.g., hot-tipped or drill-tipped catheters)rely on very aggressive treatment of the occlusive material to open up apassage. Such aggressive techniques can expose the blood vessel wall tosignificant injury, for example, vessel perforation.

The present invention is also concerned with the removal of benign ormalignant tumors in the head and neck, such as neuromas, meninges,neuroepithelial tumors, lymphomas, metastatic tumors and the like.Unfortunately, conventional techniques for removing such tumors, such aselectrosurgery, powered instruments and lasers, are not very precise,and they often cause damage or necrosis to surrounding or underlyingbody structures, which can be extremely problematic in the brain.Moreover, it is often difficult to differentiate between the targettumor tissue, and other neighboring body structures, such as cartilage,bone or nerves. In particular, many tumors in the head and neck arelocated closely adjacent to nerves. Nerve injury can lead to muscleparalysis, pain, exaggerated reflexes, loss of bladder control, impairedcough reflexes, spasticity and other conditions. Thus, the surgeonutilizing conventional devices must be extremely careful to avoiddamaging the nerves that extend through the target site.

Further, conventional techniques for removing such tumors generallyresult in the production of smoke in the surgical setting, termed anelectrosurgical or laser plume, which can spread intact, viablebacterial or viral particles from the tumor or lesion to the surgicalteam or to other portions of the patient's body. Numerous studies haveconfirmed that viable cells, such as papillomavirus, HIV, cancer cells,and the like, are spread to other portions of the patient's body duringthese tumor removal procedures. In conventional RF devices, for example,a high frequency voltage is applied between two electrodes in either amonopolar or bipolar mode to create intense heat at the target site thatcauses the inner cellular fluid to explode, producing a cutting effectalong the path of the device. This cutting effect generally results inthe production of smoke, or an electrosurgical plume, which can spreadbacterial or viral particles from the tissue to the surgical team or toother portions of the patient's body. In addition, the tissue is partedalong the pathway of evaporated cellular fluid, inducing undesirablecollateral tissue damage in regions surrounding the target tissue site.

SUMMARY OF THE INVENTION

The present invention provides systems, apparatus and methods forselectively applying electrical energy to structures in the brain andspinal cord. The systems and methods of the present invention areparticularly useful for treating cerebrovascular diseases, such asvessel occlusion, or for the volumetric removal or ablation ofintracranial tumors or Arteriovenous Malformations (AVM).

The method of the present invention comprises positioning anelectrosurgical probe or catheter adjacent the target site so that oneor more electrode terminal(s) and one or more return electrode(s) arebrought into at least partial contact or close proximity with a bodystructure within the patient's head or neck, such as tumor tissue or anocclusion within a blood vessel. High frequency voltage is then appliedbetween the electrode terminal(s) and return electrode(s) tovolumetrically remove or ablate at least a portion of the body structurein situ. The present invention is particularly useful for volumetricallyremoving atheromatous or thrombotic occlusions in blood vessels, orbenign or malignant tumors in the brain.

In a specific aspect of the invention, a method is provided forvolumetrically removing occlusive media from blood vessels within thebrain to treat cerebrovascular diseases. In this method, a catheter isadvanced intraluminally to the target site within the vessel such thatone or more electrode terminal(s) are positioned adjacent to or incontact with the vessel occlusion. In a preferred embodiment, anelectrically conducting fluid is directed to the target site so that thefluid is located between the electrode terminal(s) and one or morereturn electrode(s) positioned proximal to the electrode terminal(s) toprovide a current flow path from the electrode terminal(s) to the returnelectrode(s). High frequency voltage is applied between the electrodeterminal(s) and the return electrode(s) to volumetrically remove orablate at least a portion of the occlusive media.

In another aspect of the invention, a method is provided for removing orablating intracranial tumors or AVMs from a patient's brain. Anelectrosurgical instrument (i.e., catheter or probe) is guided to thetarget site in a conventional manner, i.e., percutaneously,transluminally or using other minimally invasive or open surgerytechniques. The target site in the brain may be charted with a varietyof imaging techniques, such as computerized tomography (CT) scanning,magnetic resonance imaging (MRI), ultrasound, angiography,radionucleotide imaging, electroencephalography (EEG) and the like. Inconjunction with one of these imaging procedures, typically CT or MRI,the present invention may also use compatible stereotactic systems forguiding the instrument to the target location. Once the distal end ofthe instrument is positioned adjacent the target site, an electricallyconducting fluid is directed thereto to provide the current flow pathbetween the electrode terminal(s) and the return electrode. The highfrequency voltage is sufficient to volumetrically remove the tumor whileminimizing the collateral damage to surrounding tissue and/or nerveswithin the brain. In specific embodiments, the high frequency voltage issufficient to effect the dissociation or disintegration of organicmolecules into non-viable atoms and molecules. Specifically, the presentinvention converts the solid tissue cells into non-condensable gasesthat are no longer intact or viable, and thus, not capable of seedingcancerous cells to other portions of the body structure. A more completedescription of this phenomena can be found in commonly assigned,co-pending U.S. application Ser. No. 09/109,219, previously incorporatedherein by reference.

In preferred embodiments, the material, e.g., tumor or occlusive media,is removed by molecular dissociation or disintegration processes. Inthese embodiments, the high frequency voltage applied to the electrodeterminal(s) is sufficient to vaporize an electrically conductive fluid(e.g., gel or saline) between the electrode terminal(s) and the tissue.Within the vaporized fluid, an ionized plasma is formed and chargedparticles (e.g., electrons) are accelerated towards the tissue to causethe molecular breakdown or disintegration of several cell layers of thetissue. This molecular dissociation is accompanied by the volumetricremoval of the tissue. The short range of the accelerated chargedparticles within the plasma layer confines the molecular dissociationprocess to the surface layer to minimize damage and necrosis to theunderlying tissue. This process can be precisely controlled to effectthe volumetric removal of tissue as thin as 10 to 150 microns withminimal heating of, or damage to, surrounding or underlying tissuestructures. A more complete description of this phenomena is describedin commonly assigned U.S. Pat. No. 5,683,366.

In yet another aspect of the invention, a method is provided fortreating aneurysms within a patient's brain. In this method, a flowablesubstance, such as collagen, is delivered to the site of an aneurysm,and an electrosurgical instrument is positioned at the target site inone of the manners described above. A high frequency voltage differenceis applied between one or more electrode terminal(s) and one or morereturn electrode(s) at or near the target site. The high frequencyvoltage difference is sufficient to harden the substance such that thehardened substance covers the weak region of the blood vessel wallcausing the aneurysm. The hardened substance may also provide a baseonto which epithelial cells of the blood vessel may grow, providing anew and stronger blood vessel wall. In preferred embodiments, anelectrically conductive fluid is delivered to the target site to providea conductive path between the electrode terminal(s) and the returnelectrode(s).

Apparatus according to the present invention generally include anelectrosurgical instrument having a shaft with proximal and distal ends,one or more electrode terminal(s) at the distal end and one or moreconnectors coupling the electrode terminal(s) to a source of highfrequency electrical energy. In some embodiments, the instrument willcomprise a catheter designed for percutaneous and/or transluminaldelivery to the brain. In other embodiments, the instrument willcomprise a more rigid probe designed for percutaneous or direct deliveryto the brain in either open procedures or port access type procedures.In both embodiments, the apparatus will include a high frequency powersupply for applying a high frequency voltage to the electrodeterminal(s). The voltage is sufficient to volumetrically remove at leasta portion of the tissue or occlusive mass in situ while minimizingdamage to the healthy tissue.

The apparatus will preferably further include a fluid delivery elementfor delivering electrically conducting fluid to the electrodeterminal(s) and the target site. The fluid delivery element may belocated on the instrument, e.g., a fluid lumen or tube, or it may bepart of a separate instrument. Alternatively, an electrically conductinggel or spray, such as a saline electrolyte or other conductive gel, maybe applied to the target site. In this embodiment, the apparatus may nothave a fluid delivery element. In both embodiments, the electricallyconducting fluid will preferably generate a current flow path betweenthe electrode terminal(s) and one or more return electrode(s). In anexemplary embodiment, the return electrode is located on the instrumentand spaced a sufficient distance from the electrode terminal(s) tosubstantially avoid or minimize current shorting therebetween and toshield the return electrode from tissue at the target site.

In a specific configuration, the electrosurgical instrument will includean electrically insulating electrode support member, preferably aninorganic support material (e.g., ceramic, glass, glass/ceramic, etc.)having a tissue treatment surface at the distal end of the instrumentshaft. One or more electrode terminal(s) are coupled to, or integralwith, the electrode support member such that the electrode terminal(s)are spaced from the return electrode. In one embodiment, the instrumentincludes an electrode array having a plurality of electrically isolatedelectrode terminals embedded into the electrode support member such thatthe electrode terminals extend about 0.0 mm to about 10 mm distally fromthe tissue treatment surface of the electrode support member. In thisembodiment, the probe will further include one or more lumens fordelivering electrically conductive fluid and/or aspirating the targetsite to one or more openings around the tissue treatment surface of theelectrode support member. In an exemplary embodiment, the lumen willextend through a fluid tube exterior to the probe shaft that endsproximal to the return electrode.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of an electrosurgical system incorporatinga power supply and an electrosurgical probe for tissue ablation,resection, incision, contraction and for vessel hemostasis according tothe present invention.

FIG. 2 is a side view of an electrosurgical probe according to thepresent invention.

FIG. 3 is an end view of the probe of FIG. 2.

FIG. 4 is a cross sectional view of the electrosurgical probe of FIG. 1.

FIG. 5 is an exploded view of a proximal portion of the electrosurgicalprobe.

FIG. 6 is a perspective view of an alternative electrosurgical probeincorporating an inner fluid lumen.

FIGS. 7A-7C are cross-sectional views of the distal portions of threedifferent embodiments of an electrosurgical probe according to thepresent invention.

FIG. 8 is a cross-sectional view of the distal tip of an electrosurgicalprobe, illustrating electric field lines between the active and returnelectrodes;

FIG. 9 is an enlarged cross-sectional view of the distal tip of anelectrosurgical probe, illustrating a vapor layer formed between theactive electrodes and the target tissue;

FIG. 10 is a perspective view of an electrosurgical catheter system forremoving body structures according to the present invention;

FIG. 11 illustrates the distal portion of an electrosurgical catheterfor use with the system of FIG. 10;

FIG. 12A and 12B are cross-sectional and end views, respectively of adistal portion of a second electrosurgical catheter according to thepresent invention;

FIG. 13 illustrates a method of treating a blood vessel in the brainaccording to the present invention;

FIG. 14 illustrates a method of removing occlusive media within a bloodvessel in the brain;

FIG. 15 is a sagittal section of the brain illustrating a method ofremoving a tumor according to the present invention;

FIGS. 16 and 17 illustrate methods for performing the present inventionin conjunction with frame and frameless sterotactic guiding methods.

FIG. 18 illustrates a method of treating an aneurysm according to thepresent invention.

DESCRIPTION OF SPECIFIC EMBODIMENTS

The present invention provides systems and methods for selectivelyapplying electrical energy to a target location within or on a patient'sbody, particularly including tissue in the brain and spinal cord. Themethods and apparatus of the present invention are also useful forremoving atheromatous material which partially or fully occludes a bodylumen, such as a blood vessel within the brain. In fact, the methods andapparatus disclosed herein may be used in a wide variety of procedures,including open procedures, intravascular procedures, urology,laparascopy, arthroscopy, thoracoscopy or other cardiac procedures,dermatology, orthopedics, gynecology, otorhinolaryngology, spinal andother neurologic procedures, oncology and the like. For convenience, theremaining disclosure will be directed specifically to the removal ofundesirable material from the brain,

In the present invention, high frequency (RF) electrical energy isapplied to one or more electrode terminals in the presence ofelectrically conductive fluid to remove and/or modify the structure oftissue structures. Depending on the specific procedure, the presentinvention may be used to: (1) volumetrically remove tissue, tumors,bone, occlusive media, cartilage or the like (i.e., ablate or effectmolecular dissociation of the body structure); (2) cut or resect bodystructures; (3) shrink or contract collagen connective tissue; and/or(4) coagulate severed blood vessels.

The techniques of the present invention will typically be performed inconjunction with instrument guiding technology for guiding the surgicalinstrument to the target site within the head and neck, e.g., the brain.In this regard, the present invention may use a variety of imagingtechniques, such as computerized tomography (CT) scanning, magneticresonance imaging (MRI), ultrasound, angiography, radionucleotideimaging, electroencephalography (EEG) and the like. In conjunction withone of these imaging procedures, typically CT or MRI, the presentinvention may also use compatible stereotactic systems for guiding theinstrument to the target location. In standard stereotactic systems, aframe, e.g., a Leksell, Todd-Wells or Guiot frame, fixes the patient'shead to the image. These frames, combined with radiological landmarksand a brain atlas, provide anatomical localization to within +−1 mm.Alternatively, imaged guided frameless stereotactic systems that utilizemodern imaging, elaborate computer software and a locating device, maybe employed with the present invention.

The techniques of the present invention may be performed percutaneouslyby introducing an electrosurgical instrument into the patient'svasculature and advancing the instrument transluminally to a targetsite. These procedures may also be performed through other ninimallyinvasive methods, such as introducing a surgical probe and endoscopethrough a small opening, e.g., a burr hole, in the patient's cranium, orthrough natural openings in the patient's head, such as transoral ortransphenoidal procedures. The present invention may further beperformed using traditional open surgery techniques.

In one aspect of the invention, the tissue or occlusive material isvolumetrically removed or ablated. In this procedure, a high frequencyvoltage difference is applied between one or more electrode terminal(s)and one or more return electrode(s) to develop high electric fieldintensities in the vicinity of the target tissue. The high electricfield intensities adjacent the electrode terminal(s) lead to electricfield induced molecular breakdown of target tissue through moleculardissociation (rather than thermal evaporation or carbonization).Applicant believes that the tissue structure is volumetrically removedthrough molecular disintegration of larger organic molecules intosmaller molecules and/or atoms, such as hydrogen, oxygen, oxides ofcarbon, hydrocarbons and nitrogen compounds. This moleculardisintegration completely removes the tissue structure, as opposed todehydrating the tissue material by the removal of liquid within thecells of the tissue, as is typically the case with electrosurgicaldesiccation and vaporization.

The high electric field intensities may be generated by applying a highfrequency voltage that is sufficient to vaporize an electricallyconducting fluid over at least a portion of the electrode terminal(s) inthe region between the distal tip of the electrode terminal(s) and thetarget tissue. The electrically conductive fluid may be a liquid, suchas isotonic saline or blood, delivered to the target site, or a viscousfluid, such as a gel, applied to the target site. Since the vapor layeror vaporized region has a relatively high electrical impedance, itincreases the voltage differential between the electrode terminal tipand the tissue and causes ionization within the vapor layer due to thepresence of an ionizable species (e.g., sodium when isotonic saline isthe electrically conducting fluid). This ionization, under optimalconditions, induces the discharge of energetic electrons and photonsfrom the vapor layer and to the surface of the target tissue. Thisenergy may be in the form of energetic photons (e.g., ultravioletradiation), energetic particles (e.g., electrons) or a combinationthereof. A more detailed description of this phenomena, termedCoblation™ can be found in commonly assigned U.S. Pat. No. 5,683,366 thecomplete disclosure of which is incorporated herein by reference.

In some procedures, e.g., treatment of aneurysms, it is desired to applysufficient thermal energy to a hardenable substance, such as collagen,to harden (e.g., shrink or contract) the substance at the target site.In these procedures, the RF energy heats the fluid substance directly byvirtue of the electrical current flow therethrough, and/or indirectlythrough the exposure of the fluid substance to fluid heated by RFenergy, to elevate the substance temperature from normal bodytemperatures (e.g., 37° C.) to temperatures in the range of 45° C. to90° C., preferably in the range from about 60° C. to 70° C. Thermalshrinkage of collagen fibers, for example, occurs within a smalltemperature range which, for mammalian collagen is in the range from 60°C. to 70° C. (Deak, G., et al., “The Thermal Shrinkage Process ofCollagen Fibres as Revealed by Polarization Optical Analysis ofTopooptical Staining Reactions,” Acta Morphologica Acad. Sci. ofHungary, Vol. 15(2), pp 195-208, 1967). Collagen fibers typicallyundergo thermal shrinkage in the range of 60° C. to about 70° C.Previously reported research has attributed thermal shrinkage ofcollagen to the cleaving of the internal stabilizing cross-linkageswithin the collagen matrix (Deak, ibid). It has also been reported thatwhen the collagen temperature is increased above 70° C., the collagenmatrix begins to relax again and the shrinkage effect is reversedresulting in no net shrinkage (Allain, J. C., et al., “IsometricTensions Developed During the Hydrothermal Swelling of Rat Skin,”Connective Tissue Research, Vol. 7, pp 127-133, 1980). A more detaileddescription of collagen shrinkage can be found in U.S. patentapplication Ser. No. 08/942,580, filed Oct. 2, 1997, entitled “SYSTEMSAND METHODS FOR ELECTROSURGICAL TISSUE CONTRACTION”, previouslyincorporated herein by reference.

In other embodiments, the present invention applies high frequency (RF)electrical energy in an electrically conducting fluid environment toremove (i.e., resect, cut or ablate) a tissue structure and to sealtransected vessels within the region of the target tissue. The presentinvention is particularly useful for sealing larger arterial vessels,e.g., on the order of 1 mm or greater. In some embodiments, a highfrequency power supply is provided having an ablation mode, wherein afirst voltage is applied to an electrode terminal sufficient to effectmolecular dissociation or disintegration of the tissue, and acoagulation mode, wherein a second, lower voltage is applied to anelectrode terminal (either the same or a different electrode) sufficientto achieve hemostasis of severed vessels within the tissue. In otherembodiments, an electrosurgical instrument is provided having one ormore coagulation electrode(s) configured for sealing a severed vessel,such as an arterial vessel, and one or more electrode terminalsconfigured for either contracting the collagen fibers within the tissueor removing (ablating) the tissue, e.g., by applying sufficient energyto the tissue to effect molecular dissociation. In the latterembodiments, the coagulation electrode(s) may be configured such that asingle voltage can be applied to coagulate with the coagulationelectrode(s), and to ablate with the electrode terminal(s). In otherembodiments, the power supply is combined with the coagulationinstrument such that the coagulation electrode is used when the powersupply is in the coagulation mode (low voltage), and the electrodeterminal(s) are used when the power supply is in the ablation mode(higher voltage).

In one method of the present invention, one or more electrode terminalsare brought into close proximity to tissue at a target site, and thepower supply is activated in the ablation mode such that sufficientvoltage is applied between the electrode terminals and the returnelectrode to volumetrically remove the tissue through moleculardissociation, as described below. During this process, vessels withinthe tissue will be severed. Smaller vessels will be automatically sealedwith the system and method of the present invention. Larger vessels, andthose with a higher flow rate, such as arterial vessels, may not beautomatically sealed in the ablation mode. In these cases, the severedvessels may be sealed by activating a control (e.g., a foot pedal) toreduce the voltage of the power supply into the coagulation mode. Inthis mode, the electrode terminals may be pressed against the severedvessel to provide sealing and/or coagulation of the vessel.

Alternatively, a coagulation electrode located on the same or adifferent instrument may be pressed against the severed vessel. Once thevessel is adequately sealed, the surgeon activates a control (e.g.,another foot pedal) to increase the voltage of the power supply backinto the ablation mode.

The present invention is also useful for removing or ablating tissuearound nerves, such as spinal, or cranial nerves, e.g., optic nerve,facial nerves, vestibulocochlear nerves and the like. This isparticularly advantageous when removing certain brain tumors that arelocated close to cranial nerves. One of the significant drawbacks withthe prior art microdebriders and lasers is that these devices do notdifferentiate between the target tissue and the surrounding nerves orbone. Therefore, the surgeon must be extremely careful during theseprocedures to avoid damage to the bone or nerves within and around thenasal cavity. In the present invention, the Coblation™ process forremoving tissue results in extremely small depths of collateral tissuedamage as discussed above. This allows the surgeon to remove tissueclose to a nerve without causing collateral damage to the nerve fibers.

In addition to the generally precise nature of the novel mechanisms ofthe present invention, applicant has discovered an additional method ofensuring that adjacent nerves are not damaged during tissue removal.According to the present invention, systems and methods are provided fordistinguishing between the fatty tissue immediately surrounding nervefibers and the normal tissue that is to be removed during the procedure.Nerves usually comprise a connective tissue sheath, or epineurium,enclosing the bundles of nerve fibers, each bundle being surrounded byits own sheath of connective tissue (the perineurium) to protect thesenerve fibers. The outer protective tissue sheath or epineurium typicallycomprises a fatty tissue (e.g., adipose tissue) having substantiallydifferent electrical properties than the normal target tissue, such asthe turbinates, polyps, mucus tissue or the like, that are, for example,removed from the nose during sinus procedures. The system of the presentinvention measures the electrical properties of the tissue at the tip ofthe probe with one or more electrode terminal(s). These electricalproperties may include electrical conductivity at one, several or arange of frequencies (e.g., in the range from 1 kHz to 100 MHz),dielectric constant, capacitance or combinations of these. In thisembodiment, an audible signal may be produced when the sensingelectrode(s) at the tip of the probe detects the fatty tissuesurrounding a nerve, or direct feedback control can be provided to onlysupply power to the electrode terminal(s) either individually or to thecomplete array of electrodes, if and when the tissue encountered at thetip or working end of the probe is normal tissue based on the measuredelectrical properties.

In one embodiment, the current limiting elements (discussed in detailabove) are configured such that the electrode terminals will shut downor turn off when the electrical impedance reaches a threshold level.When this threshold level is set to the impedance of the fatty tissuesurrounding nerves, the electrode terminals will shut off whenever theycome in contact with, or in close proximity to, nerves. Meanwhile, theother electrode terminals, which are in contact with or in closeproximity to nasal tissue, will continue to conduct electric current tothe return electrode. This selective ablation or removal of lowerimpedance tissue in combination with the Coblation™ mechanism of thepresent invention allows the surgeon to precisely remove tissue aroundnerves or bone. Applicant has found that the present invention iscapable of volumetrically removing tissue closely adjacent to nerveswithout impairment the function of the nerves, and without significantlydamaging the tissue of the epineurium. One of the significant drawbackswith the prior art microdebriders, RF devices and lasers is that thesedevices do not differentiate between the target tissue and thesurrounding nerves or bone. Therefore, the surgeon must be extremelycareful during these procedures to avoid damage to the bone or nerveswithin and around the nasal cavity. In the present invention, theCoblation™ process for removing tissue results in extremely small depthsof collateral tissue damage as discussed above. This allows the surgeonto remove tissue close to a nerve without causing collateral damage tothe nerve fibers.

In addition to the above, applicant has discovered that the Coblation™mechanism of the present invention can be manipulated to ablate orremove certain tissue structures, while having little effect on othertissue structures. As discussed above, the present invention uses atechnique of vaporizing electrically conductive fluid to form a plasmalayer or pocket around the electrode terminal(s), and then inducing thedischarge of energy from this plasma or vapor layer to break themolecular bonds of the tissue structure. Based on initial experiments,applicants believe that the free electrons within the ionized vaporlayer are accelerated in the high electric fields near the electrodetip(s). When the density of the vapor layer (or within a bubble formedin the electrically conducting liquid) becomes sufficiently low (i;e.,less than approximately 10²⁰ atoms/cm³ for aqueous solutions), theelectron mean free path increases to enable subsequently injectedelectrons to cause impact ionization within these regions of low density(i.e., vapor layers or bubbles). Energy evolved by the energeticelectrons (e.g., 4 to 5 eV) can subsequently bombard a molecule andbreak its bonds, dissociating a molecule into free radicals, which thencombine into final gaseous or liquid species.

The energy evolved by the energetic electrons may be varied by adjustinga variety of factors, such as: the number of electrode terminals;electrode size and spacing; electrode surface area; asperities and sharpedges on the electrode surfaces; electrode materials; applied voltageand power; current limiting means, such as inductors; electricalconductivity of the fluid in contact with the electrodes; density of thefluid; and other factors. Accordingly, these factors can be manipulatedto control the energy level of the excited electrons. Since differenttissue structures have different molecular bonds, the present inventioncan be configured to break the molecular bonds of certain tissue, whilehaving too low an energy to break the molecular bonds of other tissue.For example, fatty tissue, (e.g., adipose) tissue has double bonds thatrequire a substantially higher energy level than 4 to 5 eV to break.Accordingly, the present invention in its current configurationgenerally does not ablate or remove such fatty tissue. Of course,factors may be changed such that these double bonds can also be brokenin a similar fashion as the single bonds (e.g., increasing voltage orchanging the electrode configuration to increase the current density atthe electrode tips). A more complete description of this phenomena canbe found in co-pending U.S. patent application Ser. No. 09/032,375,filed Feb. 27, 1998, the complete disclosure of which is incorporatedherein by reference.

The present invention also provides systems, apparatus and methods forselectively removing brain tumors or other undesirable body structureswhile minimizing the spread of viable cells from the tumor. Conventionaltechniques for removing such tumors generally result in the productionof smoke in the surgical setting, termed an electrosurgical or laserplume, which can spread intact, viable bacterial or viral particles fromthe tumor or lesion to the surgical team or to other portions of thepatient's body. This potential spread of viable cells or particles hasresulted in increased concerns over the proliferation of certaindebilitating and fatal diseases, such as hepatitis, herpes, HIV andpapillomavirus. In the present invention, high frequency voltage isapplied between the electrode terminal(s) and one or more returnelectrode(s) to volumetrically remove at least a portion of the tissuecells in the tumor through the dissociation or disintegration of organicmolecules into non-viable atoms and molecules. Specifically, the presentinvention converts the solid tissue cells into non-condensable gasesthat are no longer intact or viable, and thus, not capable of spreadingviable tumor particles to other portions of the patient's brain or tothe surgical staff. The high frequency voltage is preferably selected toeffect controlled removal of these tissue cells while minimizingsubstantial tissue necrosis to surrounding or underlying tissue. A morecomplete description of this phenomena can be found in co-pending U.S.patent application Ser. No. 09/109,219, filed Jun. 30, 1998, thecomplete disclosure of which is incorporated herein by reference

The electrosurgical instrument will comprise a shaft having a proximalend and a distal end which supports one or more electrode terminal(s).The shaft may assume a wide variety of configurations, with the primarypurpose being to mechanically support one or more electrode terminal(s)and permit the treating physician to manipulate the electrode(s) from aproximal end of the shaft. Usually, an electrosurgical probe shaft willbe a narrow-diameter rod or tube, more usually having dimensions whichpermit it to be introduced through a burr hole, flap of bone cut or thelike in the patient's cranium, or through a conventional transoral ortransphenoidal route. Thus, the probe shaft will typically have a lengthof at least 5 cm for open procedures and at least 10 cm, more typicallybeing 20 cm, or longer for endoscopic procedures. The probe shaft willtypically have a diameter of at least 1 mm and frequently in the rangefrom 1 to 10 mm.

The electrosurgical instrument may be delivered percutaneously and/orendoluminally to the brain by insertion through a conventional orspecialized guide catheter, or the invention may include a catheterhaving an active electrode or electrode array integral with its distalend. The catheter shaft may be rigid or flexible, with flexible shaftsoptionally being combined with a generally rigid external tube formechanical support. Flexible shafts may be combined with pull wires,shape memory actuators, and other known mechanisms for effectingselective deflection of the distal end of the shaft to facilitatepositioning of the electrode or electrode array. The catheter haft willusually include a plurality of wires or other conductive elementsrunning axially therethrough to permit connection of the electrode orelectrode array and the return electrode to a connector at the proximalend of the catheter shaft. The catheter shaft may include a guide wirefor guiding the catheter to the target site, or the catheter maycomprise a steerable guide catheter. The catheter may also include asubstantially rigid distal end portion to increase the torque control ofthe distal end portion as the catheter is advanced further into thepatient's body. Specific shaft designs will be described in detail inconnection with the figures hereinafter.

The electrode terminal(s) are preferably supported within or by aninorganic insulating support positioned near the distal end of theinstrument shaft. The return electrode may be located on the instrumentshaft, on another instrument or on the external surface of the patient(i.e., a dispersive pad). The close proximity of nerves and othersensitive tissue in the brain, however, makes a bipolar design morepreferable because this minimizes the current flow through brain tissueand surrounding nerves. Accordingly, the return electrode is preferablyeither integrated with the catheter body, or another instrument locatedin close proximity to the distal end of the catheter body. The proximalend of the catheter will include the appropriate electrical connectionsfor coupling the return electrode(s) and the electrode terminal(s) to ahigh frequency power supply, such as an electrosurgical generator.

The current flow path between the electrode terminals and the returnelectrode(s) may be generated by submerging the tissue site in anelectrical conducting fluid (e.g., within a viscous fluid, such as anelectrically conductive gel) or by directing an electrically conductingfluid along a fluid path to the target site (i.e., a liquid, such asisotonic saline, or a gas, such as argon). The conductive gel may alsobe delivered to the target site to achieve a slower more controlleddelivery rate of conductive fluid. In addition, the viscous nature ofthe gel may allow the surgeon to more easily contain the gel around thetarget site (e.g., rather than attempting to contain isotonic saline). Amore complete description of an exemplary method of directingelectrically conducting fluid between the active and return electrodesis described in U.S. Pat. No. 5,697,281, previously incorporated hereinby reference. Alternatively, the body's natural conductive fluids, suchas blood, may be sufficient to establish a conductive path between thereturn electrode(s) and the electrode terminal(s), and to provide theconditions for establishing a vapor layer, as described above. However,conductive fluid that is introduced into the patient is generallypreferred over blood because blood will tend to coagulate at certaintemperatures. Advantageously, a liquid electrically conductive fluid(e.g., isotonic saline) may be used to concurrently “bathe” the targettissue surface to provide an additional means for removing any tissue,and to cool the region of the target tissue ablated in the previousmoment.

The power supply may include a fluid interlock for interrupting power tothe electrode terminal(s) when there is insufficient conductive fluidaround the electrode terminal(s). This ensures that the instrument willnot be activated when conductive fluid is not present, minimizing thetissue damage that may otherwise occur. A more complete description ofsuch a fluid interlock can be found in commonly assigned, co-pendingU.S. application Ser. No. 09/058,336, filed Apr. 10, 1998, the completedisclosure of which is incorporated herein by reference.

In some procedures, it may also be necessary to retrieve or aspirate theelectrically conductive fluid and/or the non-condensable gaseousproducts of ablation. For example, in procedures in and around the brainand its surrounding blood vessels, it may be desirable to aspirate thefluid so that it does not flow downstream. In addition, it may bedesirable to aspirate small pieces of tissue or other body structuresthat are not completely disintegrated by the high frequency energy, orother fluids at the target site, such as blood, mucus, the gaseousproducts of ablation, etc. Accordingly, the system of the presentinvention may include one or more suction lumen(s) in the instrument, oron another instrument, coupled to a suitable vacuum source foraspirating fluids from the target site. In addition, the invention mayinclude one or more aspiration electrode(s) coupled to the distal end ofthe suction lumen for ablating, or at least reducing the volume of,non-ablated tissue fragments that are aspirated into the lumen. Theaspiration electrode(s) function mainly to inhibit clogging of the lumenthat may otherwise occur as larger tissue fragments are drawn therein.The aspiration electrode(s) may be different from the ablation electrodeterminal(s), or the same electrode(s) may serve both functions. A morecomplete description of instruments incorporating aspirationelectrode(s) can be found in commonly assigned, co-pending patentapplication entitled “Systems And Methods For Tissue Resection, AblationAnd Aspiration”, filed Jan. 21, 1998, the complete disclosure of whichis incorporated herein by reference.

As an alternative or in addition to suction, it may be desirable tocontain the excess electrically conductive fluid, tissue fragmentsand/or gaseous products of ablation at or near the target site with acontainment apparatus, such as a basket, retractable sheath or the like.This embodiment has the advantage of ensuring that the conductive fluid,tissue fragments or ablation products do not flow through the patient'svasculature or into other portions of the body. In addition, it may bedesirable to limit the amount of suction to limit the undesirable effectsuction may have on hemostasis of severed blood vessels.

The present invention may use a single active electrode terminal or anarray of electrode terminals spaced around the distal surface of acatheter or probe. In the latter embodiment, the electrode array usuallyincludes a plurality of independently current-limited and/orpower-controlled electrode terminals to apply electrical energyselectively to the target tissue while limiting the unwanted applicationof electrical energy to the surrounding tissue and environment resultingfrom power dissipation into surrounding electrically conductive fluids,such as blood, normal saline, and the like. The electrode terminals maybe independently current-limited by isolating the terminals from eachother and connecting each terminal to a separate power source that isisolated from the other electrode terminals. Alternatively, theelectrode terminals may be connected to each other at either theproximal or distal ends of the catheter to form a single wire thatcouples to a power source.

In one configuration, each individual electrode terminal in theelectrode array is electrically insulated from all other electrodeterminals in the array within said instrument and is connected to apower source which is isolated from each of the other electrodeterminals in the array or to circuitry which limits or interruptscurrent flow to the electrode terminal when low resistivity material(e.g., blood, electrically conductive saline irrigant or electricallyconductive gel) causes a lower impedance path between the returnelectrode and the individual electrode terminal. The isolated powersources for each individual electrode terminal may be separate powersupply circuits having internal impedance characteristics which limitpower to the associated electrode terminal when a low impedance returnpath is encountered. By way of example, the isolated power source may bea user selectable constant current source. In this embodiment, lowerimpedance paths will automatically result in lower resistive heatinglevels since the heating is proportional to the square of the operatingcurrent times the impedance. Alternatively, a single power source may beconnected to each of the electrode terminals through independentlyactuatable switches, or by independent current limiting elements, suchas inductors, capacitors, resistors and/or combinations thereof. Thecurrent limiting elements may be provided in the instrument, connectors,cable, controller or along the conductive path from the controller tothe distal tip of the instrument. Alternatively, the resistance and/orcapacitance may occur on the surface of the active electrode terminal(s)due to oxide layers which form selected electrode terminals (e.g.,titanium or a resistive coating on the surface of metal, such asplatinum).

The tip region of the instrument may comprise many independent electrodeterminals designed to deliver electrical energy in the vicinity of thetip. The selective application of electrical energy to the conductivefluid is achieved by connecting each individual electrode terminal andthe return electrode to a power source having independently controlledor current limited channels. The return electrode(s) may comprise asingle tubular member of conductive material proximal to the electrodearray at the tip which also serves as a conduit for the supply of theelectrically conducting fluid between the active and return electrodes.Alternatively, the instrument may comprise an array of return electrodesat the distal tip of the instrument (together with the activeelectrodes) to maintain the electric current at the tip. The applicationof high frequency voltage between the return electrode(s) and theelectrode array results in the generation of high electric fieldintensities at the distal tips of the electrode terminals withconduction of high frequency current from each individual electrodeterminal to the return electrode. The current flow from each individualelectrode terminal to the return electrode(s) is controlled by eitheractive or passive means, or a combination thereof, to deliver electricalenergy to the surrounding conductive fluid while minimizing energydelivery to surrounding (non-target) tissue.

The application of a high frequency voltage between the returnelectrode(s) and the electrode terminal(s) for appropriate timeintervals effects cutting, removing, ablating, shaping, contracting orotherwise modifying the target tissue. The tissue volume over whichenergy is dissipated (i.e., a high current density exists) may beprecisely controlled, for example, by the use of a multiplicity of smallelectrode terminals whose effective diameters or principal dimensionsrange from about 10 mm to 0.01 mm, preferably from about 2 mm to 0.05mm, and more preferably from about 1 mm to 0.1 mm. Electrode areas forboth circular and non-circular terminals will have a contact area (perelectrode terminal) below 50 mm² for electrode arrays and as large as 75mm² for single electrode embodiments, preferably being in the range from0.0001 mm² to 1 mm², and more preferably from 0.005 mm² to 0.5². Thecircumscribed area of the electrode array is in the range from 0.25 mm²to 75 mm², preferably from 0.5 mm² to 40 mm², and will usually includeat least one electrode terminal and in some embodiments includes atleast two isolated electrode terminals, often at least five electrodeterminals, often greater than 10 electrode terminals and even 50 or moreelectrode terminals, disposed over the distal contact surfaces on theshaft. The use of small diameter electrode terminals increases theelectric field intensity and reduces the extent or depth of tissueheating as a consequence of the divergence of current flux lines whichemanate from the exposed surface of each electrode terminal.

The area of the tissue treatment surface can vary widely, and the tissuetreatment surface can assume a variety of geometries, with particularareas and geometries being selected for specific applications. Theactive electrode surface(s) can have area(s) in the range from 0.25 mm²to 75 mm², usually being from about 0.5 mm² to 40 mm². The geometriescan be planar, concave, convex, hemispherical, conical, linear “in-line”array or virtually any other regular or irregular shape. Most commonly,the active electrode(s) or electrode terminal(s) will be formed at thedistal tip of the electrosurgical instrument shaft, frequently beingplanar, disk-shaped, or hemispherical surfaces for use in reshapingprocedures or being linear arrays for use in cutting. Alternatively oradditionally, the active electrode(s) may be formed on lateral surfacesof the electrosurgical instrument shaft (e.g., in the manner of aspatula), facilitating access to certain body structures in endoscopicprocedures.

In some embodiments, the electrode support and the fluid outlet may berecessed from an outer surface of the instrument or handpiece to confinethe electrically conductive fluid to the region immediately surroundingthe electrode support. In addition, the shaft may be shaped so as toform a cavity around the electrode support and the fluid outlet. Thishelps to assure that the electrically conductive fluid will remain incontact with the electrode terminal(s) and the return electrode(s) tomaintain the conductive path therebetween. In addition, this will helpto maintain a vapor layer and subsequent plasma layer between theelectrode terminal(s) and the tissue at the treatment site throughoutthe procedure, which reduces the thermal damage that might otherwiseoccur if the vapor layer were extinguished due to a lack of conductivefluid. Provision of the electrically conductive fluid around the targetsite also helps to maintain the tissue temperature at desired levels.

The electrically conducting fluid should have a threshold conductivityto provide a suitable conductive path between the return electrode andthe electrode terminal(s). The electrical conductivity of the fluid (inunits of milliSiemans per centimeter or mS/cm) will usually be greaterthan 0.2 mS/cm, preferably will be greater than 2 mS/cm and morepreferably greater than 10 mS/cm. In an exemplary embodiment, theelectrically conductive fluid is isotonic saline, which has aconductivity of about 17 mS/cm.

The voltage difference applied between the return electrode(s) and theelectrode terminal(s) will be at high or radio frequency, typicallybetween about 5 kHz and 20 MHz, usually being between about 30 kHz and2.5 MHz, preferably being between about 50 kHz and 500 kHz, morepreferably less than 350 kHz, and most preferably between about 100 kHzand 200 kHz. The RMS (root mean square) voltage applied will usually bein the range from about 5 volts to 1000 volts, preferably being in therange from about 10 volts to 500 volts depending on the electrodeterminal size, the operating frequency and the operation mode of theparticular procedure or desired effect on the tissue (i.e., contraction,coagulation, cutting or ablation). Typically, the peak-to-peak voltagefor ablation or cutting will be in the range of 10 to 2000 volts andpreferably in the range of 200 to 1800 volts and more preferably in therange of about 300 to 1500 volts, often in the range of about 500 to 900volts peak to peak (again, depending on the electrode size, theoperating frequency and the operation mode). Lower peak-to-peak voltageswill be used for tissue coagulation or collagen contraction and willtypically be in the range from 50 to 1500, preferably 100 to 1000 andmore preferably 120 to 600 volts peak-to-peak.

As discussed above, the voltage is usually delivered in a series ofvoltage pulses or alternating current of time varying voltage amplitudewith a sufficiently high frequency (e.g., on the order of 5 kHz to 20MHz) such that the voltage is effectively applied continuously (ascompared with e.g., lasers claiming small depths of necrosis, which aregenerally pulsed about 10 to 20 Hz). In addition, the duty cycle (i.e.,cumulative time in any one-second interval that energy is applied) is onthe order of about 50% for the present invention, as compared withpulsed lasers which typically have a duty cycle of about 0.0001%.

The preferred power source of the present invention delivers a highfrequency current selectable to generate average power levels rangingfrom several milliwatts to tens of watts per electrode, depending on thevolume of target tissue being heated, and/or the maximum allowedtemperature selected for the instrument tip. The power source allows theuser to select the voltage level according to the specific requirementsof a particular neurosurgery procedure, cardiac surgery, arthroscopicsurgery, dermatological procedure, ophthalmic procedures, open surgeryor other endoscopic surgery procedure. For cardiac procedures andpotentially for neurosurgery, the power source may have an additionalfilter, for filtering leakage voltages at frequencies below 100 kHz,particularly voltages around 60 kHz. Alternatively, a power sourcehaving a higher operating frequency, e.g., 300 to 500 kHz may be used incertain procedures in which stray low frequency currents may beproblematic. A description of one suitable power source can be found inco-pending patent applications Ser. Nos. 09/058,571 and 09/058,336,filed Apr. 10, 1998, the complete disclosure of both applications areincorporated herein by reference for all purposes.

The power source may be current limited or otherwise controlled so thatundesired heating of the target tissue or surrounding (non-target)tissue does not occur. In a presently preferred embodiment of thepresent invention, current limiting inductors are placed in series witheach independent electrode terminal, where the inductance of theinductor is in the range of 10 uH to 50,000 uH, depending on theelectrical properties of the target tissue, the desired tissue heatingrate and the operating frequency. Alternatively, capacitor-inductor (LC)circuit structures may be employed, as described previously in U.S. Pat.No. 5,697,909, the complete disclosure of which is incorporated hereinby reference. Additionally, current limiting resistors may be selected.Preferably, these resistors will have a large positive temperaturecoefficient of resistance so that, as the current level begins to risefor any individual electrode terminal in contact with a low resistancemedium (e.g., saline irrigant or blood), the resistance of the currentlimiting resistor increases significantly, thereby minimizing the powerdelivery from said electrode terminal into the low resistance medium(e.g., saline irrigant or blood).

It should be clearly understood that the invention is not limited toelectrically isolated electrode terminals, or even to a plurality ofelectrode terminals. For example, the array of active electrodeterminals may be connected to a single lead that extends through thecatheter shaft to a power source of high frequency current.Alternatively, the instrument may incorporate a single electrode thatextends directly through the catheter shaft or is connected to a singlelead that extends to the power source. The active electrode(s) may haveball shapes (e.g., for tissue vaporization and desiccation), twizzleshapes (for vaporization and needle-like cutting), spring shapes (forrapid tissue debulking and desiccation), twisted metal shapes, annularor solid tube shapes or the like. Alternatively, the electrode(s) maycomprise a plurality of filaments, rigid or flexible brush electrode(s)(for debulking a tumor, such as a fibroid, bladder tumor or a prostateadenoma), side-effect brush electrode(s) on a lateral surface of theshaft, coiled electrode(s) or the like.

In one embodiment, an electrosurgical catheter or probe comprises asingle active electrode terminal that extends from an insulating member,e.g., ceramic, at the distal end of the shaft. The insulating member ispreferably a tubular structure that separates the active electrodeterminal from a tubular or annular return electrode positioned proximalto the insulating member and the active electrode. In anotherembodiment, the catheter or probe includes a single active electrodethat can be rotated relative to the rest of the catheter body, or theentire catheter may be rotated related to the lead. The single activeelectrode can be positioned adjacent the abnormal tissue and energizedand rotated as appropriate to remove this tissue.

The current flow path between the electrode terminal(s) and the returnelectrode(s) may be generated by submerging the tissue site in anelectrical conducting fluid (e.g., within a viscous fluid, such as anelectrically conductive gel) or by directing an electrically conductingfluid along a fluid path to the target site (i.e., a liquid, such asisotonic saline, or a gas, such as argon). This latter method isparticularly effective in a dry environment (i.e., the tissue is notsubmerged in fluid) because the electrically conducting fluid provides asuitable current flow path from the electrode terminal to the returnelectrode.

Referring to FIG. 1, an exemplary electrosurgical system 11 fortreatment of tissue in the brain and spinal cord will now be describedin detail. Electrosurgical system 11 is generally useful for minimallyinvasive procedures within the brain, wherein a surgical instrument isintroduced through a burr hole or other percutaneous penetration, orthrough a natural opening in the patient (e.g., transoral ortransphenoidal procedures). System 11 generally comprises anelectrosurgical handpiece or probe 10 connected to a power supply 28 forproviding high frequency voltage to a target site and a fluid source 21for supplying electrically conducting fluid 50 to probe 10. In addition,electrosurgical system 11 may include an endoscope (not shown) with afiber optic head light for viewing the surgical site, if desired. Theendoscope may be integral with probe 10, or it may be part of a separateinstrument. The system 11 may also include a vacuum source (not shown)for coupling to a suction lumen or tube 220 (see FIG. 2) in the probe 10for aspirating the target site.

As shown, probe 10 generally includes a proximal handle 19 and anelongate shaft 18 having an array 12 of electrode terminals 58 at itsdistal end. A connecting cable 34 has a connector 26 for electricallycoupling the electrode terminals 58 to power supply 28. The electrodeterminals 58 are electrically isolated from each other and each of theterminals 58 is connected to an active or passive control network withinpower supply 28 by means of a plurality of individually insulatedconductors (not shown). A fluid supply tube 15 is connected to a fluidtube 14 of probe 10 for supplying electrically conductive fluid 50 tothe target site. Conductive fluid 50 may be driven by gravity or with asuitable pump.

Power supply 28 has an operator controllable voltage level adjustment 30to change the applied voltage level, which is observable at a voltagelevel display 32. Power supply 28 also includes first, second and thirdfoot pedals 37, 38, 39 and a cable 36 which is removably coupled topower supply 28. The foot pedals 37, 38, 39 allow the surgeon toremotely adjust the energy level applied to electrode terminals 58. Inan exemplary embodiment, first foot pedal 37 is used to place the powersupply into the “ablation” mode and second foot pedal 38 places powersupply 28 into the “subablation” mode (e.g., coagulation, tissuecontraction or the like). The third foot pedal 39 allows the user toadjust the voltage level within the “ablation” mode. In the ablationmode, a sufficient voltage is applied to the electrode terminals toestablish the requisite conditions for molecular dissociation of thetissue (i.e., vaporizing a portion of the electrically conductive fluid,ionizing charged particles within the vapor layer and accelerating thesecharged particles against the tissue). As discussed above, the requisitevoltage level for ablation will vary depending on the number, size,shape and spacing of the electrodes, the distance in which theelectrodes extend from the support member, etc. Once the surgeon placesthe power supply in the “ablation” mode, voltage level adjustment 30 orthird foot pedal 39 may be used to adjust the voltage level to adjustthe degree or aggressiveness of the ablation.

Of course, it will be recognized that the voltage and modality of thepower supply may be controlled by other input devices. However,applicant has found that foot pedals are convenient methods ofcontrolling the power supply while manipulating the probe during asurgical procedure.

In the subablation mode, the power supply 28 applies a low enoughvoltage to the electrode terminals to avoid vaporization of theelectrically conductive fluid and subsequent molecular dissociation ofthe tissue. The surgeon may automatically toggle the power supplybetween the ablation and subablation modes by alternatively stepping onfoot pedals 37, 38, respectively. This allows, for example, the surgeonto quickly move between coagulation and ablation in situ, without havingto remove his/her concentration from the surgical field or withouthaving to request an assistant to switch the power supply. By way ofexample, as the surgeon is sculpting soft tissue in the ablation mode,the probe typically will simultaneously seal and/or coagulation smallsevered vessels within the tissue. However, larger vessels, or vesselswith high fluid pressures (e.g., arterial vessels) may not be sealed inthe ablation mode. Accordingly, the surgeon can simply step on footpedal 38, automatically lowering the voltage level below the thresholdlevel for ablation, and apply sufficient pressure onto the severedvessel for a sufficient period of time to seal and/or coagulate thevessel. After this is completed, the surgeon may quickly move back intothe ablation mode by stepping on foot pedal 37. A specific design of asuitable power supply for use with the present invention can be found inco-pending patent applications Ser. Nos. 09/058,571 and 09/058,336,filed Apr. 10, 1998, previously incorporated herein by reference.

FIGS. 2-5 illustrate an exemplary electrosurgical probe 90 constructedaccording to the principles of the present invention. As shown in FIG.2, probe 90 generally includes an elongated shaft 100 which may beflexible or rigid, a handle 204 coupled to the proximal end of shaft 100and an electrode support member 102 coupled to the distal end of shaft100. Shaft 100 preferably comprises a plastic material that is easilymolded into the shape shown in FIG. 1. Alternatively, shaft 100 maycomprise an electrically conducting material, usually metal, which isselected from the group comprising tungsten, stainless steel alloys,platinum or its alloys, titanium or its alloys, molybdenum or itsalloys, and nickel or its alloys. In this embodiment, shaft 100 includesan electrically insulating jacket, which is typically formed as one ormore electrically insulating sheaths or coatings, such aspolytetrafluoroethylene, polyimide, and the like. The provision of theelectrically insulating jacket over the shaft prevents direct electricalcontact between these metal elements and any adjacent body structure orthe surgeon. Such direct electrical contact between a body structure(e.g., tendon) and an exposed electrode could result in unwanted heatingand necrosis of the structure at the point of contact causing necrosis.

Handle 204 typically comprises a plastic material that is easily moldedinto a suitable shape for handling by the surgeon. Handle 204 defines aninner cavity (not shown) that houses the electrical connections 250(FIG. 5), and provides a suitable interface for connection to anelectrical connecting cable 22 (see FIG. 1). Electrode support member102 extends from the distal end of shaft 100 (usually about 1 to 20 mm),and provides support for a plurality of electrically isolated electrodeterminals 104 (see FIGS. 3 and 4). As shown in FIG. 2, a fluid tube 233extends through an opening in handle 204, and includes a connector 235for connection to a fluid supply source, for supplying electricallyconductive fluid to the target site. Depending on the configuration ofthe distal surface of shaft 100, fluid tube 233 may extend through asingle lumen (not shown) in shaft 100, or it may be coupled to aplurality of lumens (also not shown) that extend through shaft 100 to aplurality of openings at its distal end. In the representativeembodiment, fluid tube 233 extends along the exterior of shaft 100 to apoint just proximal of return electrode 112 (see FIG. 4). In thisembodiment, the fluid is directed through an opening 237 past returnelectrode 112 to the electrode terminals 104. Probe 90 may also includea valve 17 (FIG. 1) or equivalent structure for controlling the flowrate of the electrically conducting fluid to the target site.

As shown in FIG. 2, the distal portion of shaft 100 is preferably bentto improve access to the operative site of the tissue being treated.Electrode support member 102 has a substantially planar tissue treatmentsurface 212 (FIG. 3) that is usually at an angle of about 10 to 90degrees relative to the longitudinal axis of shaft 100, although theshaft may have no angle at all. In alternative embodiments, the distalportion of shaft 100 comprises a flexible material which can bedeflected relative to the longitudinal axis of the shaft. Suchdeflection may be selectively induced by mechanical tension of a pullwire, for example, or by a shape memory wire that expands or contractsby externally applied temperature changes.

In the embodiment shown in FIGS. 2-5, probe 90 includes a returnelectrode 112 for completing the current path between electrodeterminals 104 and a high frequency power supply 28 (see FIG. 1). Asshown, return electrode 112 preferably comprises an annular conductiveband coupled to the distal end of shaft 100 slightly proximal to tissuetreatment surface 212 of electrode support member 102, typically about0.5 to 10 mm and more preferably about 1 to 10 mm. In embodiments wherethe shaft comprises a conductive material, the shaft will have anexposed portion that functions as the return electrode. Return electrode112 is coupled to a connector (not shown) that extends to the proximalend of probe 10, where it is suitably connected to power supply 10 (FIG.1).

As shown in FIG. 2, return electrode 112 is not directly connected toelectrode terminals 104. To complete this current path so that electrodeterminals 104 are electrically connected to return electrode 112,electrically conducting fluid (e.g., isotonic saline) is caused to flowtherebetween. In the representative embodiment, the electricallyconducting fluid is delivered through fluid tube 233 to opening 237, asdescribed above. Alternatively, the fluid may be delivered by a fluiddelivery element (not shown) that is separate from probe 90. Inarthroscopic surgery, for example, the body cavity will be flooded withisotonic saline and the probe 90 will be introduced into this floodedcavity. Electrically conducting fluid will be continually resupplied tomaintain the conduction path between return electrode 112 and electrodeterminals 104.

In alternative embodiments, the fluid path may be formed in probe 90 by,for example, an inner lumen or an annular gap between the returnelectrode and a tubular support member within shaft 100 (see FIG. 6).This annular gap may be formed near the perimeter of the shaft 100 suchthat the electrically conducting fluid tends to flow radially inwardtowards the target site, or it may be formed towards the center of shaft100 so that the fluid flows radially outward. In both of theseembodiments, a fluid source (e.g., a bag of fluid elevated above thesurgical site or suitable pumping device), is coupled to probe 90 via afluid supply tube (not shown) that may or may not have a controllablevalve.

Referring to FIG. 3, the electrically isolated electrode terminals 104are spaced apart over tissue treatment surface 212 of electrode supportmember 102. The tissue treatment surface and individual electrodeterminals 104 will usually have dimensions within the ranges set forthabove. In the representative embodiment, the tissue treatment surface212 has a circular cross-sectional shape with a diameter in the range ofabout 1 to 20 mm. The individual electrode terminals 104 preferablyextend outward from tissue treatment surface 212 by a distance of about0.0 to 4 mm, usually about 0.2 to 2 mm. Applicant has found that thisconfiguration increases the high electric field intensities andassociated current densities around electrode terminals 104 tofacilitate the ablation of tissue as described in detail above.

In the embodiment of FIGS. 2-5, the probe includes a single, largeropening 209 in the center of tissue treatment surface 212, and aplurality of electrode terminals (e.g., about 3 to 15 electrodeterminals) around the perimeter of surface 212 (see FIG. 3).Alternatively, the probe may include a single, annular, or partiallyannular, electrode terminal at the perimeter of the tissue treatmentsurface. The central opening 209 is coupled to a suction lumen 215within shaft 100 and a suction tube 211 (FIG. 2) for aspirating tissue,fluids, and/or gases from the target site. In this embodiment, theelectrically conductive fluid generally flows radially inward pastelectrode terminals 104 and then back through the opening 209.Aspirating the electrically conductive fluid during surgery allows thesurgeon to see the target site, and it prevents the dispersal of gases,tissue fragments and/or calcified deposits into the patient's body.

In some embodiments, the probe 90 will also include one or moreaspiration electrode(s) (not shown) coupled to the aspiration lumen 215for inhibiting clogging during aspiration of tissue fragments from thesurgical site. A more complete description of these embodiments can befound in commonly assigned co-pending application Ser. No. 09/010,382,filed Jan. 21, 1998, the complete disclosure of which is incorporatedherein by reference for all purposes.

FIG. 5 illustrates the electrical connections 250 within handle 204 forcoupling electrode terminals 104 and return electrode 112 to the powersupply 28. As shown, a plurality of wires 252 extend through shaft 100to couple terminals 104 to a plurality of pins 254, which are pluggedinto a connector block 256 for coupling to a connecting cable 22 (FIG.1). Similarly, return electrode 112 is coupled to connector block 256via a wire 258 and a pin 260.

According to the present invention, the probe 90 further includes anidentification element that is characteristic of the particularelectrode assembly so that the same power supply 28 can be used fordifferent electrosurgical operations. In one embodiment, for example,the probe 90 includes a voltage reduction element or a voltage reductioncircuit for reducing the voltage applied between the electrode terminals104 and the return electrode 112. The voltage reduction element servesto reduce the voltage applied by the power supply so that the voltagebetween the electrode terminals and the return electrode is low enoughto avoid excessive power dissipation into the electrically conductingmedium and/or ablation of the soft tissue at the target site. Thevoltage reduction element primarily allows the electrosurgical probe 90to be compatible with other ArthroCare generators that are adapted toapply higher voltages for ablation or vaporization of tissue. Forcontraction of tissue, for example, the voltage reduction element willserve to reduce a voltage of about 100 to 135 volts rms (which is asetting of 1 on the ArthroCare Models 970, 980 and 2000 Generators) toabout 45 to 60 volts rms, which is a suitable voltage for contraction oftissue without ablation (e.g., molecular dissociation) of the tissue.

Of course, for some procedures, the probe will typically not require avoltage reduction element. Alternatively, the probe may include avoltage increasing element or circuit, if desired.

In the representative embodiment, the voltage reduction element is adropping capacitor 262 which has first leg 264 coupled to the returnelectrode wire 258 and a second leg 266 coupled to connector block 256.Of course, the capacitor may be located in other places within thesystem, such as is in, or distributed along the length of: (1) thecable; (2) in the generator; (3) in the connector, etc. In addition, itwill be recognized that other voltage reduction elements, such asdiodes, transistors, inductors, resistors, capacitors or combinationsthereof, may be used in conjunction with the present invention. Forexample, the probe 90 may include a coded resistor (not shown) that isconstructed to lower the voltage applied between return electrode 112and electrode terminals 104 to a suitable level for contraction oftissue. In addition, electrical circuits may be employed for thispurpose.

Alternatively or additionally, the cable 22 that couples the powersupply 10 to the probe 90 may be used as a voltage reduction element.The cable has an inherent capacitance that can be used to reduce thepower supply voltage if the cable is placed into the electrical circuitbetween the power supply, the electrode terminals and the returnelectrode. In this embodiment, the cable 22 may be used alone, or incombination with one of the voltage reduction elements discussed above,e.g., a capacitor.

Further, it should be noted that the present invention can be used witha power supply that is adapted to apply a voltage within the selectedrange for treatment of tissue. In this embodiment, a voltage reductionelement or circuitry may not be desired.

FIGS. 7A-7C schematically illustrate the distal portion of threedifferent embodiments of probe 90 according to the present invention. Asshown in 7A, electrode terminals 104 are anchored in a support matrix102 of suitable insulating material (e.g., ceramic or glass material,such as alumina, silicon nitride zirconia and the like) which could beformed at the time of manufacture in a flat, hemispherical or othershape according to the requirements of a particular procedure. Thepreferred support matrix material is alumina, available from KyoceraIndustrial Ceramics Corporation, Elkgrove, Ill., because of its highthermal conductivity, good thermal shock resistance, good electricallyinsulative properties, high flexural modulus, resistance to carbontracking, biocompatibility, and high melting point. The support matrix102 is adhesively joined to a tubular support member 78 that extendsmost or all of the distance between matrix 102 and the proximal end ofprobe 90. Tubular member 78 preferably comprises an electricallyinsulating material, such as an epoxy or silicone-based material.

In a preferred construction technique, electrode terminals 104 extendthrough pre-formed openings in the support matrix 102 so that theyprotrude above tissue treatment surface 212 by the desired distance. Theelectrodes are then bonded to the tissue treatment surface 212 ofsupport matrix 102, typically by an inorganic sealing material 80.Sealing material 80 is selected to provide effective electricalinsulation, and good adhesion to both the alumina matrix 102 and theelectrode terminals (e.g., titanium, tungsten, molybdenum, platinum,etc.). Sealing material 80 additionally should have a compatible thermalexpansion coefficient and a melting point well below that of the metalelectrode terminals and the ceramic support matrix, typically being aglass or glass ceramic.

In the embodiment shown in FIG. 7A, return electrode 112 comprises anannular member positioned around the exterior of shaft 100 of probe 90.Return electrode 90 may fully or partially circumscribe tubular supportmember 78 to form an annular gap 54 therebetween for flow ofelectrically conducting fluid 50 therethrough, as discussed below. Gap54 preferably has a width in the range of 0.1 mm to 4 mm. Alternatively,probe may include a plurality of longitudinal ribs between supportmember 78 and return electrode 112 to form a plurality of fluid lumensextending along the perimeter of shaft 100. In this embodiment, theplurality of lumens will extend to a plurality of openings.

Return electrode 112 is disposed within an electrically insulativejacket 18, which is typically formed as one or more electricallyinsulative sheaths or coatings, such as polytetrafluoroethylene,polyamide, and the like. The provision of the electrically insulativejacket 18 over return electrode 112 prevents direct electrical contactbetween return electrode 112 and any adjacent body structure. Suchdirect electrical contact between a body structure (e.g., tendon) and anexposed electrode member 112 could result in unwanted heating andnecrosis of the structure at the point of contact causing necrosis.

As shown in FIG. 7A, return electrode 112 is not directly connected toelectrode terminals 104. To complete this current path so that terminals104 are electrically connected to return electrode 112, electricallyconducting fluid 50 (e.g., isotonic saline) is caused to flow alongfluid path(s) 83. Fluid path 83 is formed by annular gap 54 betweenouter return electrode 112 and tubular support member 78. Theelectrically conducting fluid 50 flowing through fluid path 83 providesa pathway for electrical current flow between electrode terminals 104and return electrode 112, as illustrated by the current flux lines 60 inFIG. 6A. When a voltage difference is applied between electrodeterminals 104 and return electrode 112, high electric field intensitieswill be generated at the distal tips of terminals 104 with current flowfrom terminals 104 through the target tissue to the return electrode,the high electric field intensities causing ablation of tissue 52 inzone 88.

FIG. 7B illustrates another alternative embodiment of electrosurgicalprobe 90 which has a return electrode 112 positioned within tubularmember 78. Return electrode 112 is preferably a tubular member definingan inner lumen 57 for allowing electrically conducting fluid 50 (e.g.,isotonic saline) to flow therethrough in electrical contact with returnelectrode 112. In this embodiment, a voltage difference is appliedbetween electrode terminals 104 and return electrode 112 resulting inelectrical current flow through the electrically conducting fluid 50 asshown by current flux lines 60 (FIG. 3). As a result of the appliedvoltage difference and concomitant high electric field intensities atthe tips of electrode terminals 104, tissue 52 becomes ablated ortransected in zone 88.

FIG. 7C illustrates another embodiment of probe 90 that is a combinationof the embodiments in FIGS. 7A and 7B. As shown, this probe includesboth an inner lumen 57 and an outer gap or plurality of outer lumens 54for flow of electrically conductive fluid. In this embodiment, thereturn electrode 112 may be positioned within tubular member 78 as inFIG. 7B, outside of tubular member 78 as in FIG. 7A, or in bothlocations.

FIG. 8 illustrates the current flux lines associated with an electricfield 120 applied between the active and return electrodes 104, 112 whena voltage is applied therebetween. As shown, the electric fieldintensity is substantially higher in the region 88 at the tip of theelectrode 58 because the current flux lines are concentrated in theseregions. This high electric field intensity leads to induced molecularbreakdown of the target tissue through molecular dissociation. As aresult of the applied voltage difference between electrode terminal(s)104 and the target tissue 52(i.e., the voltage gradient across theplasma layer 124), charged particles (not shown) in the plasma (viz.,electrons) are accelerated towards the tissue. At sufficiently highvoltage differences, these charged particles gain sufficient energy tocause dissociation of the molecular bonds within tissue structures. Thismolecular dissociation is accompanied by the volumetric removal (i.e.,ablative sublimation) of tissue and the production of low molecularweight gases 126 (see FIG. 9), such as oxygen, nitrogen, carbon dioxide,hydrogen and methane. The short range of the accelerated chargedparticles within the tissue confines the molecular dissociation processto the surface layer to minimize damage and necrosis to the underlyingtissue.

Referring to FIGS. 10-12, the electrosurgical device according to thepresent invention may also be configured as an elongate catheter system400 including portions with sufficient flexibility to permitintroduction into the body and to the target site through one or morevascular lumen(s). As shown in FIG. 10, a catheter system 400 generallycomprises an electrosurgical catheter 460 connected to a power supply 28by an interconnecting cable 486 for providing high frequency voltage toa target tissue site and an irrigant reservoir or source 600 forproviding electrically conducting fluid to the target site. Catheter 460generally comprises an elongate, flexible shaft body 462 including atissue removing or ablating region 464 at the distal end of body 462.The proximal portion of catheter 460 includes a multi-lumen fitment 614which provides for interconnections between lumens and electrical leadswithin catheter 460 and conduits and cables proximal to fitment 614. Byway of example, a catheter electrical connector 496 is removablyconnected to a distal cable connector 494 which, in turn, is removablyconnectable to generator 28 through connector 492. One or moreelectrically conducting lead wires (not shown) within catheter 460extend between one or more active electrodes 463 at tissue ablatingregion 464 and one or more corresponding electrical terminals (also notshown) in catheter connector 496 via active electrode cable branch 487.Similarly, one or more return electrodes 466 at tissue ablating region464 are coupled to a return electrode cable branch 489 of catheterconnector 496 by lead wires (not shown). Of course, a single cablebranch (not shown) may be used for both active and return electrodes.

Catheter body 462 may include reinforcing fibers or braids (not shown)in the walls of at least the distal ablation region 464 of body 462 toprovide responsive torque control for rotation of electrode terminalsduring tissue engagement. This rigid portion of the catheter body 462preferably extends only about 7 to 10 mm while the remainder of thecatheter body 462 is flexible to provide good trackability duringadvancement and positioning of the electrodes adjacent target tissue.

Conductive fluid 30 is provided to tissue ablation region 464 ofcatheter 460 via a lumen (not shown in FIG. 10) within catheter 460.Fluid is supplied to lumen from the source along a conductive fluidsupply line 602 and a conduit 603, which is coupled to the innercatheter lumen at multi-lumen fitment 614. The source of conductivefluid (e.g., isotonic saline) may be an irrigant pump system (not shown)or a gravity-driven supply, such as an irrigant reservoir 600 positionedseveral feet above the level of the patient and tissue ablating region8. A control valve 604 may be positioned at the interface of fluidsupply line 602 and conduit 603 to allow manual control of the flow rateof electrically conductive fluid 30. Alternatively, a metering pump orflow regulator may be used to precisely control the flow rate of theconductive fluid.

System 400 further includes an aspiration or vacuum system (not shown)to aspirate liquids and gases from the target site. The aspirationsystem will usually comprise a source of vacuum coupled to fitment 614by a aspiration connector 605.

FIGS. 11 and 12 illustrate the working end 464 of an electrosurgicalcatheter 460 constructed according to the principles of the presentinvention. As shown in FIG. 11, catheter 460 generally includes anelongated shaft 462 which may be flexible or rigid, and an electrodesupport member 620 coupled to the distal end of shaft 462. Electrodesupport member 620 extends from the distal end of shaft 462 (usuallyabout 1 to 20 mm), and provides support for a plurality of electricallyisolated electrode terminals 463. Electrode support member 620 andelectrode terminals 463 are preferably secured to a tubular supportmember 626 within shaft 460 by adhesive 630.

The electrode terminals 463 may be constructed using round, square,rectangular or other shaped conductive metals. By way of example, theelectrode terminal materials may be selected from the group includingstainless steel, tungsten and its alloys, molybdenum and its alloys,titanium and its alloys, nickel-based alloys, as well as platinum andits alloys. Electrode support member 620 is preferably a ceramic, glassor glass/ceramic composition (e.g., aluminum oxide, titanium nitride).Alternatively, electrode support member 620 may include the use ofhigh-temperature biocompatible plastics such as polyether-ether-keytone(PEEK) manufactured by Vitrex International Products, Inc. orpolysulfone manufactured by GE Plastics. The adhesive 630 may, by way ofexample, be an epoxy (e.g., Master Bond EP42HT manufactured by MasterBond) or a silicone-based adhesive.

As shown in FIG. 12B, a total of 7 circular active electrodes orelectrode terminals 463 are shown in a symmetrical pattern having anactive electrode diameter, D₁ in the range from 0.05 mm to 1.5 mm, morepreferably in the range from 0.1 mm to 0.75 mm. The interelectrodespacings, W₁ and W₂ are preferably in the range from 0.1 mm to 1.5 mmand more preferably in the range from 0.2 mm to 0.75 mm. The distancebetween the outer perimeter of the electrode terminal 463 and theperimeter of the electrode support member, W₃ is preferably in the rangefrom 0.1 mm to 1.5 mm and more preferably in the range from 0.2 mm to0.75 mm. The overall diameter, D₂ of the working end 464 of catheterbody 462 is preferably in the range from 0.5 mm to 10 mm and morepreferably in the range from 0.5 mm to 5 mm. As discussed above, theshape of the active electrodes may be round , square, triangular,hexagonal, rectangular, tubular, flat strip and the like and may bearranged in a circularly symmetric pattern as shown in FIG. 12B or may,by way of example, be arranged in a rectangular pattern, square pattern,or strip.

Catheter body 462 includes a tubular cannula 626 extending along body462 radially outward from support member 620 and electrode terminals463. The material for cannula 626 may be advantageously selected from agroup of electrically conductive metals so that the cannula 626functions as both a structural support member for the array of electrodeterminals 463 as well as a return electrode 624. The support member 626is connected to an electrical lead wire (not shown) at its proximal endwithin a connector housing (not shown) and continues via a suitableconnector to power supply 28 to provide electrical continuity betweenone output pole of high frequency generator 28 and said return electrode624. The cannula 626 may be selected from the group including stainlesssteel, copper-based alloys, titanium or its alloys, and nickel-basedalloys. The thickness of the cannula 626 is preferably in the range from0.08 mm to 1.0 mm and more preferably in the range from 0.05 mm to 0.4mm.

As shown in FIGS. 11 and 12A, cannula 626 is covered with anelectrically insulating sleeve 608 to protect the patient's body fromthe electric current. Electrically insulating sleeve 608 may be acoating (e.g., nylon) or heat shrinkable plastic (e.g., fluropolymer orpolyester). As shown in FIG. 12A, the proximal portion of the cannula626 is left exposed to function as the return electrode 624. The lengthof the return electrode 624, L₅ is preferably in the range from 1 mm to30 mm and more preferably in the range from 2 mm to 20 mm. The spacingbetween the most distal portion of the return electrode 624 and theplane of the tissue treatment surface 622 of the electrode supportmember 620, L₁ is preferably in the range from 0.5 mm to 30 mm and morepreferably in the range from 1 mm to 20 mm. The thickness of theelectrically insulating sleeve 608 is preferably in the range from 0.01mm to 0.5 mm and more preferably in the range from 0.02 mm to 0.2 mm.

In the embodiment shown in FIG. 11, the fluid path is formed in catheterby an inner lumen 627 or annular gap between the return electrode 624and a second tubular support member 628 within shaft 460. This annulargap may be formed near the perimeter of the shaft 460 as shown in FIG.11 such that the electrically conducting fluid tends to flow radiallyinward towards the target site, or it may be formed towards the centerof shaft 460 (not shown) so that the fluid flows radially outward. Inboth of these embodiments, a fluid source (e.g., a bag of fluid elevatedabove the surgical site or having a pumping device), is coupled tocatheter 460 via a fluid supply tube (not shown) that may or may nothave a controllable valve.

In an alternative embodiment shown in FIG. 12A, the electricallyconducting fluid is delivered from a fluid delivery element (not shown)that is separate from catheter 460. In arthroscopic surgery, forexample, the body cavity will be flooded with isotonic saline and thecatheter 460 will be introduced into this flooded cavity. Electricallyconducting fluid will be continually resupplied to maintain theconduction path between return electrode 624 and electrode terminals463.

FIGS. 13 and 14 illustrate a method for treating cerebrovascular diseaseaccording to the present invention. Typically, a distal portion 506 ofan electrosurgical catheter 508 such as the one described above ispercutaneously introduced into the vasculature and endoluminallyadvanced into the patient's brain 500. The catheter 508 may be guided tothe target location 502 within the patient's brain using any number ofconventional or non-conventional techniques (e.g., sterotactic systems)as described above. The catheter 508 may be advanced with a variety oftechniques, such as a guidewire, steerable catheter and the like.Referring now to FIG. 14, a severe occlusion 503 in a body passage 505often completely or partially blocks the body passage, making itextremely difficult to recanalize with conventional catheter techniques.In these circumstances, it is necessary to at least partially recanalize(creating an opening through) the occlusion before conventional catheterprocedures can begin. Conventional methods for recanalizing severeocclusions include hot-tipped catheters, laser catheters, anddrill-tipped catheters. These approaches rely on very aggressivetreatment of the stenotic material, which can expose the blood vesselwall to significant injury, for example, vessel perforation.

Once the surgeon has reached the point of major blockage 503,electrically conductive fluid is delivered through one or more internallumen(s) 509 within the catheter to the tissue. In some embodiments, thecatheter may be configured to operate with a naturally occurring bodyfluid, e.g., blood, as the conductive medium. The fluid flows past thereturn electrode 520 to the electrode terminals 522 at the distal end ofthe catheter shaft. The rate of fluid flow is controlled with a valve(not shown) such that the zone between the occlusion and electrodeterminal(s) 522 is constantly immersed in the fluid. The power supply 28(FIG. 10) is then turned on and adjusted such that a high frequencyvoltage difference is applied between electrode terminals 522 and returnelectrode 520. The electrically conductive fluid provides the conductionpath (see current flux lines) between electrode terminals 522 and thereturn electrode 520.

As discussed above, the high frequency voltage is sufficient to convertthe electrically conductive fluid (not shown) between the occlusion 503and electrode terminal(s) 522 into an ionized vapor layer or plasma (notshown). As a result of the applied voltage difference between electrodeterminal(s) 522 and the occlusive media 503 (i.e., the voltage gradientacross the plasma layer), charged particles in the plasma (viz.,electrons) are accelerated towards the occlusion. At sufficiently highvoltage differences, these charged particles gain sufficient energy tocause dissociation of the molecular bonds within tissue structures. Thismolecular dissociation is accompanied by the volumetric removal (i.e.,ablative sublimation) of tissue and the production of low molecularweight gases, such as oxygen, nitrogen, carbon dioxide, hydrogen andmethane. The short range of the accelerated charged particles within thetissue confines the molecular dissociation process to the surface layerto minimize damage and necrosis to the surrounding vessel wall 504.During the process, the gases may be aspirated through catheter 508. Inaddition, excess electrically conductive fluid, and other fluids (e.g.,blood) may be aspirated from the target site to facilitate the surgeon'sview.

FIG. 15 illustrates a method for removing a brain tumor according to thepresent invention. The system and method of the present invention isparticularly useful in the ablation (i.e., disintegration) of cancercells and tissue containing cancer cells, such malignant tumors withinthe brain and spinal cord, facial tumors, other tumors in the head andneck and the like. In particular, the ability to selective ablate tissuemakes the present invention particularly useful for ablating tumorsadjacent to or on nerves. In addition, the present invention's abilityto completely disintegrate the target tissue can be advantageous in thisapplication because simply vaporizing and fragmenting cancerous tissue(as with prior art devices) may lead to spreading of viable cancer cells(i.e., seeding) to other portions of the patient's body or to thesurgical team in close proximity to the target tissue. In addition, thecancerous tissue can be removed to a precise depth while minimizingnecrosis of the underlying tissue.

As shown in FIG. 15, a burr hole 600 is formed in the patient's skull toprovide access to the brain. Of course, other methods of introductionmay be used (e.g., craniectomy, transoral or transphenoidal routes). Aworking end 602 of an electrosurgical instrument 604 is guided to thetumor 606 with a conventional or non-conventional guiding system, suchas a stereotactic frame 620 (FIG. 16) or an image guide system, such asframeless stereotaxy systems 630 (FIG. 17). Once the working end 602 ofinstrument 604 is positioned adjacent the tumor 606, electricallyconductive fluid is delivered through one or more internal lumen(s) (notshown) within the instrument 604, and a high frequency voltagedifference is applied between one or more electrode terminals 608 and areturn electrode 610 on working end 602. As discussed above, the highfrequency voltage is sufficient to convert the electrically conductivefluid (not shown) between the tumor 606 and electrode terminal(s) 522into an ionized vapor layer or plasma (not shown), which results in themolecular dissociation of tumor tissue. Since the tumor cells areconverted directly into non-viable gases, the spread of harmful tumorcells to other portions of the brain is minimized. During the process,the gases, excess electrically conductive fluid, and small non-ablatedportions of the tumor tissue mass may be aspirated through catheter 508.

The present invention also provides systems and methods for treatinganeurysms by applying RF energy to a hardenable substance, such ascollagen. An aneurysm is a localized dilation of a blood vessel,typically an arterial blood vessel. If left untreated, the aneurysmgenerally becomes worse under the fluid pressure of blood flowingthrough the blood vessel, and eventually bursts or ruptures, withcatastrophic results for the fluid-delivery capacity of the bloodvessel. When the blood vessel is critical to the operation of the brain,this rupture is catastrophic for the patient.

One known method for treating intracranial aneurysms involvespositioning small metallic coils into the bubble or pocket formed by theaneurysm outside of the main fluid flow of the blood vessel. Oncepresent at the target site, the metallic coils fill the region definedby the aneurysm to mitigate or prevent the blood flow into this region,thereby limiting or preventing further enlargement of the aneurysm.While promising, this method may not be permanent as the aneurysmremains the weak area in the blood vessel wall, and thus may requirefurther corrective action. In addition, this method is generally noteffective with blood vessel walls that have not yet formed the bubble orpocket into which the small metallic coils would be inserted.

In this embodiment, a flowable substance, e.g., collagen, is deliveredto the site of an aneurysm, and RF energy is applied to the substance toharden it to minimize or prevent enlargement of the aneurysm by blockingthe flow of blood to the region of the aneurysm. FIG. 18 illustrates asaccular aneurysm 700 located in the posterior circulation between thebasilar artery and the posterior inferior cerebella artery. According tothe present invention, a working end of an electrosurgical catheter (notshown) is delivered through the patient's vasculature to the neck region702 of the aneurysm 700. Collagen is then delivered through an internallumen of the electrosurgical catheter (or through another catheter) tothe neck region 702. It may be desirable to slow or stop the flow ofblood (e.g., with a balloon) temporarily to facilitate placement of thecollagen substance around the aneurysm 700. Once the collagen is inplace, a high frequency voltage difference is applied between one ormore electrode terminal(s) and one or more return electrodes on theworking end of the catheter. In some embodiments, conductive fluid isdelivered to the site to ensure a conductive path between the electrodeterminal(s) and the return electrode(s). In other embodiments, the bloodwith the artery may be sufficient to provide this conductive path.

The energy supplied by the high frequency voltage is selected such thatthe collagen will harden in the region of the neck 702 of the aneurysm700. The hardened collagen prevents further flow of blood into thefundus of the aneurysm, thereby limiting its growth. Of course it willbe recognized that other substances besides collagen may be used inconjunction with the RF energy.

What is claimed is:
 1. A method for treating a tumor located in the headand neck comprising: positioning an electrode terminal and a returnelectrode adjacent a body structure at a target site within a patient'shead or neck; applying a sufficient high frequency voltage differencebetween the electrode terminal and the return electrode tovolumetrically remove a portion of the body structure; effectingmolecular dissociation of at least a portion of the cells within thetumor; and converting at least a portion of the tumor cells intonon-viable gases to minimize the spread of the tumor.
 2. The method ofclaim 1 wherein the body structure comprises an occlusive media disposedwithin a body vessel.
 3. The method of claim 2 wherein the occlusivemedia is selected from the group comprising atheromatous occlusions,thrombotic occlusions, plaque and emboli.
 4. The method of claim 2further comprising applying high frequency voltage to the electrodeterminal and a return electrode positioned within the blood vessel andspaced from the occlusive media such that an electrical current flowsfrom the electrode terminal, through the region of the occlusive media,and to the return electrode.
 5. The method of claim 4 wherein the highfrequency voltage is applied in the presence of electrically conductingfluid, the method further comprising generating a current flow paththrough the electrically conducting fluid between the return electrodeand the electrode terminal to selectively ablate the occlusive media. 6.The method of claim 1 further comprising: before the applying step,fluidly isolating a region around the occlusive media within the bodypassage to confine products of ablation within said region; andaspirating said ablation products from the body passage.
 7. The methodof claim 1 wherein the body structure comprises an arteriovenousmalformation.
 8. The method of claim 1 wherein the positioning stepcomprises advancing an electrosurgical instrument through a percutaneouspenetration in the patient's head.
 9. The method of claim 1 wherein thepositioning step comprises advancing an electrosurgical cathetertransluminally into the patient's head.
 10. The method of claim 1wherein the positioning step comprises the step of guiding the electrodeterminal to the target site in the head.
 11. The method of claim 10further comprising an electrode array including a plurality ofelectrically isolated electrode terminals.
 12. The method of claim 11wherein the guiding step comprises detecting electrical properties ofbody structures adjacent each of the electrode terminals and guiding theelectrode array to the target site based on the electrical properties.13. The method of claim 12 wherein the electrical properties comprisesimpedance between each of the electrode terminals and the returnelectrode.
 14. The method of claim 11 further comprising independentlycontrolling current flow from at least two of the electrode terminalsbased on impedance between the electrode terminal and a returnelectrode.
 15. The method of claim 1 wherein the electrode terminalcomprises a single electrode at or near a distal end of anelectrosurgical instrument.
 16. The method of claim 1 wherein the returnelectrode and the electrode terminal are both located on anelectrosurgical instrument.
 17. The method of claim 1 further comprisingpositioning the electrode terminal and the return electrode withinelectrically conductive fluid.
 18. The method of claim 17 furthercomprising applying sufficient voltage to the electrode terminal in thepresence of the electrically conducting fluid to vaporize at least aportion of the fluid between the electrode terminal and the tissuestructure.
 19. The method of claim 18 further comprising acceleratingcharged particles from the vaporized fluid to the tissue structure tocause dissociation of the molecular bonds within the tissue structure.20. The method of claim 17 further comprising positioning the electrodeterminal and the return electrode within electrically conductive fluidto generate a current flow path between the return electrode and theelectrode terminal.
 21. A method for treating tissue in the head andneck comprising: positioning an electrode array including a plurality ofelectrically isolated electrode terminals and a return electrodeadjacent a body structure at a target site within a patient's head orneck; applying a sufficient high frequency voltage difference betweenthe electrode terminals and the return electrode to volumetricallyremove a portion of the body structure; and detecting electricalproperties of body structures adjacent each of the electrode terminalsand guiding the electrode array to the target site based on theelectrical properties.
 22. The method of claim 21 wherein the bodystructure comprises an occlusive media disposed within a body vessel.23. The method of claim 22 wherein the occlusive media is selected fromthe group comprising atheromatous occlusions, thrombotic occlusions,plaque and emboli.
 24. The method of claim 21 further comprisingapplying high frequency voltage to the electrode terminals and thereturn electrode positioned within the blood vessel and spaced from theocclusive media such that an electrical current flows from the electrodeterminals, through the region of the occlusive media, and to the returnelectrode.
 25. The method of claim 21 wherein the high frequency voltageis applied in the presence of electrically conducting fluid, the methodfurther comprising generating a current flow path through theelectrically conducting fluid between the return electrode and theelectrode terminals to selectively ablate the occlusive media.
 26. Themethod of claim 21 wherein the positioning step comprises advancing anelectrosurgical instrument through a percutaneous penetration in thepatient's head.
 27. The method of claim 21 wherein the positioning stepcomprises advancing an electrosurgical catheter transluminally into thepatient's head.
 28. The method of claim 21 wherein the electricalproperties comprises impedance between each of the electrode terminalsand the return electrode.
 29. The method of claim 21 wherein the returnelectrode and the electrode terminals are both located on anelectrosurgical instrument.